Within the context of regional integration, comparative regionalism, organizational change, and regional security literatures, this book investigates three cases wherein regional economic organizations were confronted with conventional security threats: the 1978-91 Association of Southeast Asian Nations-Vietnam Standoff, the 1990 Economic Community of West Africa-Liberian Civil War Challenge, and the 1990-91 European Communities-Balkans Crisis. While the literature suggests multiple possible explanations for regional economic organizations’ response to these security challenges, including systemic and power-related factors, organizational factors and functional needs, and cognitive and social factors, the author argues that the decision to transform a regional economic organization into a conventional security actor is most influenced by decision makers’ perceptions of threat and functional necessity.